Printed in Great Britain 47 Antigenic Differences Between Wild Type and Mutants

The clear-plaque mutants, phage Agv (large plaque, virulent inducer mutant) and Agc (large clear plaque), both types isolated from the same wild-type phage A, were neutralized by antiserum to phage A + at a much slower rate than?~+. For the anti-wild-type serum the neutralization constant (K) was I I I min.-1 for phage A+, whereas for phage 2tgv it was only 27 min.-1. On the other hand, antiserum to phage;tgv neutralized all three phages at similar rates (K = 84, 76 and 70 min.-1 for Agv, Agc and h + respectively). When anti-wild-type serum (K = 96 min.- ~ for A +) was tested against 50 independent /~gv-type mutants, it gave a mean Kvalue of 28 min.- ~ with 42 of the isolates. Three of the isolates, with mean K value (93 min--~) equivalent to that for?t+, produced plaques of unusual morphology in certain conditions. With the other five;tgv isolates, the serum showed a mean K value of 53 min.-1. The same anti-wild-type serum neutralized phage Ag (large turbid plaques) at approximately the same rate (K = 34 min.-1) as the majority of the;tgv iso-lates, whereas for,~ni (minute turbid plaque) the rate was greater (K = I23 min.-x) than for A + and was intermediate (K = 44 min--~) for;tmsco (medium cocarde plaque). These results indicate that the composition r structure of tail components can vary in different phage h mutants, and this feature of the phage particle is not directly associated with loss of ability to lysogenize the host bacterium, Escherichia coli